Escherichia coli (E. coli) is a gram-negative rod-shaped bacterium. Although most strains of E. coli are benign and are found as normal intestinal flora of humans and other animals, some strains are pathogenic and can lead to sometimes-fatal disease. Different strains of pathogenic E. coli differ in their epidemiology, clinical course and potential for causing outbreaks of disease. Passage of disease is generally through the fecal/oral route.
Pathogenicity has been linked to several serotypes, as defined by O and H antigens. Different pathogenic serotypes are associated with different clinical disease courses and have associated with them different levels of concern from the standpoint of public health. Several outbreaks of disease have been tracked to food and water borne sources of pathogenic E. coli. 
One serotype in particular, serotype E. coli O157:H7, has been associated with several food and water borne outbreaks and is regulated as an adulterant in ground beef by the USDA with a zero tolerance standard.
Since E. coli is ubiquitous, and most serotypes are nonpathogenic, the ability to detect pathogenic serotypes, and to differentiate among pathogenic serotypes with different clinical and public health implications is useful.
It is desirable, therefore, to have a test for the rapid detection of pathogenic E. coli and to differentiate those of greater public health and regulatory concern.